The invention relates to the field of photonic crystals, and in particular to a dielectric high omnidirectional reflector.
Low-loss periodic dielectrics, or "photonic crystals", allow the propagation of electromagnetic energy, e.g., light, to be controlled in otherwise difficult or impossible ways. The existence of photonic bandgap in certain photonic crystals has given rise to the possibility that a photonic crystal can be a perfect mirror for light from any direction, with any polarization, within a specified frequency range. Within the frequency range of photonic bandgaps, there are no propagating solutions of Maxwell's equations inside a periodic medium. Consequently, a wave-front with a frequency within the gap which is incident upon the surface of such a crystal would be completely reflected.
It is natural to assume that a necessary condition for such omnidirectional reflection is that the photonic crystal exhibit a complete three-dimensional photonic band-gap, i.e., a frequency range within which there are no propagating solutions of Maxwell's equations. Such a photonic crystal would require periodic variations in dielectric constant in all three dimensions. These crystals, if designed for infrared or optical light, are difficult to fabricate, since the spatial periods must be comparable to the wavelength of operation. This is the reason why, despite heroic experiments involving advanced lithographic methods or self-assembling microstructures, most of the proposals for utilizing photonic crystals are in early stages of development.